The production of phenolic moldings is an old art, having involved, over the years, the use of two different types of phenol-formaldehyde condensate: novolacs and resoles. The novolacs were produced by condensing formaldehyde and phenol in a mole ratio of about 1:1 or slightly less, and usually in the presence of an acidic condensing agent. Condensation was carried essentially to completion, so that the novolac became water insoluble and could be separated from associated water and used to formulate a molding compound by mixing with a curing agent, usually hexamethylenetetraamine and other additives such as fillers, reinforcements and mold release agents. Moldings were then produced in matched molds by the "heat pressure" method disclosed an an early Baekeland patent.
Moldings have also been made by a casting technique from resoles: partial condensates of formaldehyde and phenol in a higher mole ratio, usually at least about 1.5:1; condensation is caused by heating, usually in the presence of a fixed alkali condensing agent. Condensation is interrupted at a desired end point by discontinuing heating and acidifying to a desired pH at which room temperature condensation is comparatively slow. The casting can then be produced from the partial condensate by adding a "hardener," e.g., a solution of hydrochloric or phosphoric acid in glycerine or in a glycol, and pouring the resulting composition into a mold. Cure proceeds at ambient or a slightly higher temperature. A detailed discussion of phenol-formaldehyde condensates appears in the The Chemistry of Phenolic Resins, Martin, John Wiley & Sons, Inc. 1956, and cited references. Aside from a wide variety of hydraulic cements we can also employ magnesium oxysulfate cements, magnesium oxychloride cement and gypsum cements. Briefly, hydraulic cements are those inorganic cements which set and harden by the addition of water. Specific examples of hydraulic cements include aluminous cements, masonry cements, natural cements, Portland cements, Portland blast furnace slag cements, Portland-pozzolan cement and slag cement. Preferably, Portland cement is used alone or in conjunction with the other cements.
It has also been suggested* that laminates, coatings, moldings and expanded foams can be produced from a polyhydric phenol-aldehyde resin containing 2-6 percent hydraulic cement, based on the weight of the polyhydric phenol. The cement is said to lower the viscosity of the resin and to give it high temperature strength and fire retarding properties. FNT * U.S. Pat. No. 3,502,610.